Let's try to debug this...
Your code is running to here?
Code:
TEMP:
'SNIP
    LCDOUT $FE,$C0,dta(0),DTA(1),DTA(2),DTA(3),DTA(4),DTA(5),DTA(6),DTA(7),DTA(8),dta(9),dta(10),dta(11),dta(12),DTA(13),DTA(14),DTA(15)
    RETURN
Then ends up here
Code:
main: 
'ADD LED TO FLASH TO SEE IF IT IS HERE OR DISPLAY "AT MAIN" TO THE LCD 
    if portB.1=1 then                               'arrow down
        push = push+1 : goto selection : endif
    if portA.1=1 then                               'arrow up
        push = push-1 : goto selection : endif
    pause 5000
    goto main
Then when you get here
Code:
selection:
"DISPLAY THE VALUE OF "push" TO THE LCD
    pause 200
    if push=1 then screen1
    if push=2 then screen2
    if push=3 then screen3
    if push=4 then screen4
    if push=5 then screen5
    if push=6 then screen6
    if push=7 then screen7
    if push=8 then screen8
    if push=9 then
        push = 1 : goto screen1 : endif  
    if push=0 then
        push = 8 : goto screen8 : endif
    goto main
I have a sneaky suspicion you will need to use >= in place of =
Does that make sense?